In mining, gallery roof and wall propping is being increasingly done by using the so-called "bolting method" in preference to the more classical method involving wood or steel bracing. Under the bolting method, steel rods or bolts are anchored in holes that have been bored to a diameter of 20 to 60 mm.
The rods or bolts can be anchored or sealed by one of the three following methods: (1) the so-called mechanical method, which uses a steel rod fitted with shells or plates which are expanded like an umbrella by means of wedges or by screwing, (2) the resin cartridge method and (3) the method in which resin or cement in bulk is forced into the bore as a sealing charge for a bolt.
When the bolts are sealed in with cement, preparing and inserting the charge into the prepared boring is a long and delicate operation. In addition, cements containing accelerators have very short working times once mixed with water, which makes the preparation and injection even more delicate.